What if Ed got stuck inside alter!Ed's body and didn't get Zeppelin'd? What would happen in Amestris? What if he met up with Heiderich still? And what if they met shortly after the war, instead of when they're 18/17? It would be like alter!Hyde...or something. Whoah. And all the while, Ed and alter!Ed would be battling for control over one body. And Hohenheim will be happy.
EDIT: I've been misspelling "zeppelin" again, argh.